Using the address book to navigate is extremely useful if you want to look for documents, processes or deadlines for a specific contact.
First find the desired contact in the address book and open it:
In the lower portion of the detailed contact page you will see the contact tab. Use this tab to easily find all entries linked to the contact you selected, sorted by module:
You can now look for (outstanding) invoices for this contact, for instance, or create a new invoice.
Incidentally, this is also the only way to enter notes for a specific contact.